The present invention generally relates to digital control systems and, more particularly, to a phase recovery filtering technique to alleviate spacecraft central computer or spacecraft central processor (SCP) throughput shortages.
A SCP generally plays a crucial role in controlling a spacecraft's attitude, mode and phase, fault detection, actuators and sensors, and hardware components, for example. The increasing complexity of space missions requires more software to complete a successful mission. More software puts greater demands on the spacecraft's SCP. The SCP runs or implements the software. At a certain point, the SCP will run out of the processing time needed to execute all the instructions and computations asked of it at each real time-clock interrupt (RTI). Running out of the processing time needed causes a shortage known as the SCP throughput problem.
The SCP throughput problem has plagued many projects. Typically, when the SCP throughput problem happens, the systems engineer must ask each software unit developer to do whatever possible to minimize algorithm computation or computer usage to avoid the SCP throughput problem. Past attempts to avoid the SCP throughput problem forced the redesign of the Attitude Control Subsystem (ACS). Unfortunately, a redesign is rarely feasible since higher software demands would require the ACS to be designed from scratch because the ACS is at project's end.
A request to enlarge a sampling period with multiple RTIs to gain more throughput traffic involves a complete redesign of the control law to recover the unstable phase loss due to an extra sampling time delay in the attitude control feedback loops. The ACS is designed with a pre-determined sampling time with proper stablity margins and robustness. When the SCP thoughput problem occurs, it requies the ACS to cut down on sampling time, which cannot be done at this point.
There is a need for an innovative filtering technique to recover the unstable phase margin loss due to a time delay caused by the SCP throughput problem. There is also a need for a simple and effective filtering technique to solve the SCP throughput problem with reduced project time loses and reduced costs. Moreover, there is a need for a phase recovery filtering technique to overcome the SCP throughput shortage.